Flowers tone down the iridescence of their petals and avoid confusing bees

Date: February 25, 2016

Source: University of Cambridge

Iridescent flowers are never as dramatically rainbow-coloured as iridescent beetles, birds or fish, but their petals produce the perfect signal for bees, according to a new study published today in Current Biology.

Bees buzzing around a garden, looking for nectar, need to be able to spot flower petals and recognise which coloured flowers are full of food for them. Professor Beverley Glover from the University of Cambridge's Department of Plant Sciences and Dr Heather Whitney from the University of Bristol found that iridescence -- the shiny, colour-shifting effect seen on soap bubbles -- makes flower petals more obvious to bees, but that too much iridescence confuses bees' ability to distinguish colours.

Whitney, Glover and their colleagues found that flowers use more subtle, or imperfect, iridescence on their petals, which doesn't interfere with the bees' ability to distinguish subtly different colours, such as different shades of purple. Perfect iridescence, for example as found on the back of a CD, would make it more difficult for bees to distinguish between subtle colour variations and cause them to make mistakes in their flower choices.

"In 2009 we showed that some flowers can be iridescent and that bees can see that iridescence, but since then we have wondered why floral iridescence is so much less striking than other examples of iridescence in nature," says Glover. "We have now discovered that floral iridescence is a trade-off that makes flower detection by bumblebees easier, but won't interfere with their ability to recognise different colours."

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